Conventionally, disposable toilet-training underpants described in, for example, Japanese Patent No. 3386124 have been known as such. The training underpants have a portion (hereinafter referred to as a main body portion) that extends from a front belly part to a back part via a crotch part and four side surface portions (hereinafter referred to as side pieces) that extend from both ends in the longitudinal direction of the main body portion in their width direction.
The training underpants described in Japanese Patent No. 3386124 have a pair of portions (hereinafter referred to as side portions) that covers the side surfaces of the lumbar part of a wearer, the pair of portions being formed when the respective side pieces are welded to each other by ultrasonic welding in a state that the main body portion is folded in two so that the side pieces overlap each other.
Here, Japanese Patent No. 3386124 also discloses an ultrasonic device that forms the side portions. The ultrasonic device has an anvil and an ultrasonic horn that compresses the respective side pieces between the ultrasonic horn and the anvil to weld the respective side pieces to each other by ultrasonic welding.
However, the ultrasonic device described in Japanese Patent No. 3386124 welds the respective side pieces to each other only by the anvil and the ultrasonic horn. Therefore, the welding positions of the respective side pieces cannot be accurately managed.
That is, in the ultrasonic device described in Japanese Patent No. 3386124, the respective side pieces are freely movable with respect to the ultrasonic device until the respective side pieces are compressed between the anvil and the ultrasonic horn. Therefore, the welding positions fluctuate in accordance with the positions of the respective side pieces.